Drugs may be delivered to patients by a variety of methods including oral intravenous administration, inhalation of aerosols, an epidermal patch, and subcutaneous implants. The method chosen depends, among other things, upon the desired therapeutic concentration of the drug or pharmaceutical to be achieved in the patient and the duration the concentration must be maintained.
Recently released materials and pharmaceuticals have been developed which allow a drug to be subcutaneously introduced or administered beneath the skin of a patient so that the drug is slowly released over a long period of time. Such implants allow a drug to be dispensed in a relatively uniform dose over many months or years. This method of administering drugs is becoming especially important and popular as a method of administering contraceptives.
Previously, subcutaneous implants and other types of implants have been inserted beneath the skin by use of a trocar system, which is a two piece system including a cannula and an obdurator. First, an incision is made through the skin and the cannula and obdurator are inserted together through the skin. Next, the obdurator is withdrawn, leaving the cannula in place as a guide for inserting the implant. The implant is inserted through the cannula, and the obduratoris used to push the implant to the end of the cannula. The obdurator is then used to force the implant out of the cannula while the cannula is withdrawn, such that the implant is deposited in the channel previously occupied by the cannula. The cannula and obdurator are then withdrawn completely, leaving the implant in place beneath the skin.
This trocar insertion process requires substantial expertise in coordinating the pressing of the obdurator and the withdrawing of the cannula to deposit the implant in the channel. If these two processes are not properly coordinated, the implant may be forced into the tissue so that the implant has to make its own channel as it is inserted. Forcing the implant into the tissue causes additional trauma to the tissue and may cause the implant to become damaged by the force exerted by the obdurator. This is especially true for a hydrogel implant. While subcutaneous implantation may be done surgically using a scalpel to make the incision and a trocar system to place the implant, such methods require a physician or other highly trained person. Recently improved instruments for inserting subcutaneous implants have been developed which typically require far less skill to operate, and thus may be better suited for non-surgical physicians and other less skilled individuals, and require less time to perform the implantation procedure.
U.S. Pat. No. 4,105,030 discloses an implanting apparatus for use in subcutaneously implanting multiple pellets in animals. The apparatus provides a one-handed implanting system that reduces the risk of trauma from forcing the implant into the tissue, and it also reduces contamination. The animal implant apparatus includes a handle, a needle containing the pellets to be implanted, and a rod positioned within the needle for pushing the pellets out of the needle. Once the needle containing the pellets has been inserted subcutaneously, a spring loaded trigger on the handle is activated which causes the needle to be automatically withdrawn by a spring leaving the implanted pellets in place. However, the handle configuration of this implanting device is designed for use in animals, such as cattle, and due to it's size and shape, it would be difficult to use for inserting implants subcutaneously in humans. Further, it is not possible to control the motion of the needle in this device because the needle will automatically retract upon activation of the trigger. The complex spring loaded propelling system and trigger of this implant apparatus increase the chances that the device will jam and fail to eject the pellets when required.
Contraceptive steroids that are implanted subcutaneously are normally imbedded in biologically inert polymers, some of which are biodegradable. The pellets made from such materials are typically long and cylindrical in cross section, and the size of these materials is on the order of the size of a pencil lead. The materials are generally flexible, ranging from somewhat flexible to very flexible nature. See, for example, U.S. Pat. No. 4,451,253, which describes some exemplary contraceptive pellets and an apparatus for individually implanting such pellets subcutaneously.
The size and shape of an implant pellet are important in determining the rate of delivery of a particular drug from a subcutaneous implant. Practical considerations put constraints on the dimensions of a subcutaneous implant. In particular, the length of an implant is generally limited. A typical implant is on the order of 1½ to 2 inches long. Longer implants are much more difficult to accurately locate. They are also more susceptible to breakage, which may affect the drug delivery rate and, in general, are simply more cumbersome and cosmetically apparent. Because of this, it is frequently necessary to implant a desired amount of a drug as a plurality of individual, shorter implant pellets rather than as a single longer pellet. Thus, an instrument which can quickly allow a physician or nurse to implant a plurality of pellets with minimal physical and psychological trauma to a patient would be desirable. When implanting several implants, care must be taken to accurately place the implants in a manner such that one does not interfere with the dissolution of the others.